Vector s-parameter measurements are used for fully characterizing a linear network, ensuring distortion-free transmission, designing efficient matching networks, and deriving accurate device and error models. In a generalized two-port network with characteristic impendence Z0, S11=b1/a1, describes the reflection/return loss for port 1, S12=b1/a2 describes the reverse gain/loss, S21=b2/a1 describes the gain/insertion loss, and S22=b2/a2 describes the reflection/return loss for port 2.
To determine vector s-parameter measurements, a phase detector down-converts a reference and test channels to make the measurements at a lower frequency. In this method, the phase detector requires extra hardware such as local oscillator sources, mixers, and filters to synchronize, convert and process the signals. Further, in this method, the phase detector requires complex software algorithms to calibrate the system in order to make both magnitude and phase measurements. In another method to determine vector s-parameter measurements, a six-port coupler uses at least three receivers to calculate the phase and another receiver for more accurate measurements, such as phase measurements close to zero and one-hundred eighty degrees. Further, two six-port couplers will be needed for a full two port of measurements. In addition, the six port coupler is a special purpose hardware component, which is not commonly available off the shelf. Thus, this method is problematic because it requires a complex six-port coupler which is not commonly available and because an extra receiver is required for phase measurements which are close to zero and one-hundred eighty degrees.